Skip to main content

Full text of "Text Book Of Mechanical Engineering"

See other formats

Forging a Large Crank Shaft.                131

seen at A, Fig. 126. The forgernan always requires a staffer
'porter* to carry his forging, to which, for the time at least, the.
latter is welded. It is simply a long tapering bar B (Figs. 125
and 126)7 supported by a crane chain, and carried to and from
the furnace by the undermen, while the head forgeman directs
the hammerman, and applies the different tools to the work under
the hammer. The end of the porter is put in the furnace and
made to pick up, at a white heat, a few slabs which have been
previously placed there; putting them tinder the hammer they
are all thoroughly welded, and the round form of the first part
of the shaft obtained by swages similar to those of the smith, but
of suitable size. More slabs are added, and welded, until the
shaft is sufficiently long to take the first crank web. The web is
now built up by laying slabs upon it as at c (Fig. 126), the end
being put back in the furnace. Care must be taken in piling
these slabs, both now and always, that space be. left between them
by the placing of pieces of scrap, so as to enable them to take a
welding heat right through. Bringing the hot slabs back to the
hammer, they are welded by striking both at top and sides: and
so the process is repeated on both sides, a and I) (Fig. 126),
until the shaft has the form D (Fig. 1260). It is then set down
as at E. But the web is not yet finished. Heating again, it is
flattened out to the shape F, and slabs are again piled on and
welded to the body of the material, the process being repeated
as before for both sides of the web. The object of laying the
slabs on both sides of the web is to keep the direction of the fibre
such that the crank may be best suited to meet the stress pat
upon it. By this time the forging, being unbalanced, will be
difficult to turn round; but this is overcome by clamping four
arms dd on to the porter, these being turned by the strength of
two or four men as required. The web is now hammered at top,
bottom, and sides, to correct dimensions, the ragged end e chipped
off by means of a cutter, and the other end f cut down with the
same tool, the extra piece G (Fig. 126a) being worked by sets
until drawn out to receive more slabs. The shoulder & and the
piece G, are next finished to the round by means of swages, and
the building of the second web commences. This is carried out
in exactly the same manner as the first one, except that it must